1. Field of the Invention
The present invention relates to implantable devices for delivering beneficial agents or drugs to a living body. More particularly, the present invention relates to implantable devices for metering and delivering a drug bolus to a target area in a living body in response to sensed adverse patient conditions.
2. Description of the Related Art
Cardiac arrhythmias, which are irregularities in cardiac rhythms, adversely affect millions of individuals. Atrial fibrillation is likely the most common cardiac arrhythmia and may result in dizziness, weakness and other adverse effect. Moreover, atrial fibrillation, may result in death if it leads to ventricular fibrillation. Accordingly, significant efforts have been undertaken to provide therapy to prevent or relieve atrial fibrillation. Such efforts have included drug therapy, in the form of oral or intravenous drugs, and electrical defibrillation techniques.
Implantable systems are known for detecting the onset of fibrillation and providing a patient with electronic countermeasures. For example, U.S. Pat. No. 5,817,131, which is incorporated herein by reference in its entirety, discloses an implantable atrial defibrillators which includes implements for monitoring electrical activity of the heart and providing cardioversion countermeasures as well as pain relief therapy to the central nervous system in response to detection of the onset of atrial fibrillation or other adverse conditions.
There is a current trend towards the use of implantable drug delivery systems to provide site-specific and/or sustained delivery of beneficial agents to address adverse patient conditions, such as atrial fibrillation. Such delivery systems may include implantable infusion pumps, which typically include a pressurized drug reservoir and some form of fluid flow control. One example of an implantable infusion pump is the SYNCHROMED(trademark) pump manufactured by Medtronic, Inc. of Minneapolis, Minn.
In atrial defibrillation applications, drug delivery systems must be capable of rapidly and accurately metering and delivering one or more drug boluses to a target area in response to the detection of an adverse condition, such as atrial fibrillation. Known drug infusion pumps, however, are not adapted to rapidly meter and deliver such drug boluses. There is thus a need for an implantable infusion pump which is capable of rapidly and accurately metering and delivering one or more boluses of drug in response to a detected adverse condition.
The present invention solves the aforementioned problems and others by providing an implantable pump which is capable of metering a drug bolus and delivering a drug bolus in response to a detected condition of atrial fibrillation. In a preferred embodiment, an implantable pump is provided with a control module which processes incoming signals from sensors to detect the onset of an adverse, patient condition. The pump is provided with a bolus metering assembly which is driven by a drive train in response to command signals from the control module. The bolus metering assembly includes an inlet valve which is adapted to permit ingress of pressurized drug-containing fluid from a pressurized main bellows reservoir into a collapsible auxiliary bellows that defines a bolus reservoir. An outlet valve is also provided to permit egress of the bolus of drug from the bolus reservoir after an appropriate amount of drug has accumulated therein. The inlet and outlet valves are driven by valve tappets, which are driven by a face cam, that provides the proper timing sequence for opening and closing the inlet and outlet valves. According to one aspect of the invention, the auxiliary bellows defining the bolus reservoir is exposed to the pressure in the main reservoir such that pressure in the main reservoir is used to expel the bolus of drug from the bolus reservoir.
In another embodiment, the bolus metering assembly is provided with a flow restrictor instead of an inlet valve. A cam drives the outlet valve to permit egress from the bolus reservoir after a predetermined amount of drug-containing fluid has flowed through the inlet restrictor. An auxiliary valve is provided within the auxiliary bellows reservoir and is adapted to engage an outlet port and abruptly stop the egress of the bolus when the auxiliary bellows is fully collapsed.